How do I fix this Traceback error for Massive Material Nodes?
The script you are trying to use was written to work with blender 2.66 or earlier, in 2.67 the python api changed in regards to creating new nodes.

Where the script has shader = TreeNodes.nodes.new('BSDF_DIFFUSE') it should be changed to shader = TreeNodes.nodes.new('ShaderNodeBsdfDiffuse'). There will be other similar changes needed. A list of old and new node names can be found here. Chances are there are also other changes that will also need to be done to get the script working.

As the cycles material converter is still in the contrib addons, chances are that one still works. Try the tips I gave in your other question about that script before trying to update this older script.